Munirul Hady, Taufiq Saidi, Muttaqin Hasan, Sugiarto
This research focused on refining alkali activator parameters to enhance the mechanical performance and micro-structural characteristics of diatomaceous earth (DE) based geopolymer paste. The influence of sodium hydroxide (NaOH) concentration (10, 12, and 14 M) and the sodium silicate to sodium hydroxide ratio (Na₂SiO₃/NaOH) (0.5, 1.0, and 2.0) on key response variables was evaluated using response surface methodology (RSM), including compressive strength, flexural strength, flowability, and initial setting time. The optimal mixture was identified at a NaOH concentration of 10 M and a sodium silicate proportion of 53.04% in the total activator solution, resulting in a compressive strength of 18.05 MPa and a flexural strength of 2.32 MPa. Microstructural investigations using SEM–EDS, XRD, and FTIR confirmed the formation of a compact geopolymer matrix with low porosity, predominantly composed of sodium aluminosilicate hydrate (N–A–S–H) gel. ANOVA results indicated that the Na₂SiO₃ to total activator ratio had a more significant effect on mechanical properties (p < 0.05) than NaOH molarity. Furthermore, the empirical model demonstrated strong predictive reliability, with deviations between predicted and experimental values remaining below 5%. The minimal errors in flow (0.74%) and initial setting time (1.51%) reflect accurate prediction of fresh state behavior and reaction kinetics, while the low errors in compressive (2.95%) and flexural strength (4.04%) confirm the model’s capability to estimate hardened state performance. Overall, the optimized alkali activation regime significantly improved the geopolymerization of DE, supporting its potential as a sustainable, locally sourced construction material with enhanced performance. This study presents a novel approach by simultaneously optimizing NaOH molarity and Na₂SiO₃/NaOH ratio using response surface methodology (RSM) to enhance both mechanical performance and microstructural characteristics of diatomaceous earth–based geopolymer paste, providing a comprehensive optimization framework not previously reported. © 2026, Politechnika Lubelska. All rights reserved.
Doctoral Program, School of Engineering, Post Graduate Program, Universitas Syiah Kuala, Banda Aceh, 23111, Indonesia; Department of Civil Engineering, Universitas Syiah Kuala, Banda Aceh, 23111, Indonesia
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